1. Field of the Invention
This invention relates to an electrostatic chucking (ESC) stage for holding a board-shaped object such as a substrate, and a substrate processing apparatus comprising the ESC stage.
2. Description of the Related Art
The ESC stages for chucking substrates by electrostatic force are used widely in the field of substrate processing. In manufacturing electronic devices such as LSIs (Large-Scale Integrate circuits) and display devices such as LCDs (Liquid Crystal Displays), for example, there are many steps of processing substrates that are bases for products. In these steps, ESC stages are used for securing process uniformity and process reproducibility. Taking the plasma etching as an example, a substrate is etched, utilizing functions of ions and activated species produced in plasma. In this, an ESC stage is used for holding the substrate at an optimum position against the plasma.
Generally, an ESC stage comprises a chucking electrode to which voltage for chucking is applied, and a dielectric plate that is polarized by the voltage applied to the chucking electrode. The held substrate is in contact with the dielectric plate, and chucked by static electricity induced on the surface of the dielectric plate.
ESC stages are demanded to chuck substrates with making them stable. If a substrate is displaced or changes the posture on an ESC stage while a process is carried out, it might bring the problem of degrading the process uniformity and the process reproducibility. Thermal transformation and thermal expansion of an ESC stage could be critical in substrate processing in view of process homogeneity and process reproducibility. Temperatures of substrates during processes are often higher than room temperature. This is usually from process conditions, otherwise because of environments in process chambers in which processes are carried out. Anyway, when temperature of a substrate rises up, temperature of the ESC stage rises up as well. If thermal transformation or thermal expansion of the ESC stage takes place from the temperature rise, the held substrate might be transformed or displaced.